1. Field of the Invention
The invention relates to an image handling system including an image source and an image receiver linked to each other for transfer of pixel values, the image source transferring about the pixels to the receiver on a clock of pixels after block of pixels basis. The invention also relates to a method of operating such a system.
2. Description of the Related Art
Such an image handling system and method is known from PCT patent application WO 95/14349.
Conventionally the pixel values of pixels of an image are transferred line of pixels after line of pixels from an image source like a tuner to an image receiver like a display device.
Resolution of the image receiver is a cost factor. For example, a low resolution display device which displays one output pixel for each block of pixels in the image is usually less expensive than a higher resolution display device which displays an output pixel for each pixel in the image. It is therefore desirable to introduce different versions of the image handling system, which differ from each other in the resolution used by the image receiver. However, in order to obtain the lower resolution the pixel values of the pixels from each block need to be compounded. In principle this could be done in the image source, but to simplify the exchange of different image receivers and to keep down development cost, it is desirable to keep the image source the same for each version of the image handling system. In this way only one image source needs to be developed for several image receivers and the development cost of the image receivers could be spread over different types of image sources.
However, when the pixel values are transferred for line of pixels after line of pixels one or more line memories are needed in the image receiver to store pixel values that are transferred between the pixel values of pixels of one block for later compounding. This causes extra cost, thereby defeating the purpose of using different image receivers.
What is needed is a method of allowing interchangeable use of image receivers with mutually different resolutions in the image handling system, without requiring a change in the way the pixel values are transferred and without requiring a memory in the image receiver for pixel values of pixels that do not belong to a block and that are transferred between the pixel values for that block.
WO 95/14349 teaches a system in which an image is compressed for transfer between the image source and the image receiver. The image source represents the image in a Quadtree structure, which subdivides the image into a matrix of two times two blocks, each block in turn being subdivided into a matrix of two times two smaller blocks and so on recursively. When the content of the image is such that there is less than a predetermined amount of variation in a block, the smaller blocks contained in that block are pruned from the representation of the image. The image source transfers image details only for those blocks that have not been pruned to the image receiver. In addition the image source transfers a quadtree code to indicate which blocks have been pruned. Information about the pixels is transferred block after block, all of the unpruned smaller blocks contained in each particular block in a matrix being transferred before transferring information about any other block in that matrix.
This publication is concerned with compression of images by eliminating transfer of whole blocks depending on the image content. It gives no suggestion to order the transfer of pixel values in this way if no elimination of blocks is attempted.